There's growing debate about of the use of automatic license plate readers by local police departments, as some people are worried about what departments do with the information they get.

The high-definition cameras can be mounted on a police vehicle and in a single pass, capture and read a license plate, helping police find a needle in a haystack.

"Child abduction cases have been solved. Missing person cases have been solved. Elderly people who've been lost have been found," said Elwood Police Chief Fred Hayes.

Hayes showed us how it works on one of ABC 7's news vehicles.

The image of the plate is stored along with a date, time, and location stamp.

"It will then alert the officer that perhaps this is a stolen vehicle," Hayes said.

But some see potential for abuse.

"It tells a lot of what a person does by virtue of where they've been: what doctors they've visited, what protests they've gone to, and we know that this information can be abused," said Khadine Bennett, ACLU of Illinois.

The ACLU and a bipartisan group of state lawmakers have introduced a bill requiring all data collected to be erased after 30 days.

"They don't dump the data on the license plates that aren't flagged or they don't need for a criminal investigation, so they have all of these extra license plates that are just being stored," Bennett said.